1. Field of the Invention
The present invention relates to an optical lens assembly with a filter member for image taking, and more particularly to an optical lens assembly capable of filtering the infrared band of lights of a photographed object and then forming an image by an appropriately installed optical lens assembly in order to be applied to electronic products.
2. Description of the Related Art
As optical technology advances, image reception devices becomes increasingly popular, and a large number of electronic devices such as digital cameras, mobile phones, smart phones, notebook computers or tablet PCs, are disposed with the image reception devices. Therefore, users have higher demands on image reception devices for high quality and high resolution.
In an image reception device, CCD or CMOS image sensors are generally used for capturing color images of a photographed object. Since the CCD and CMOS image sensor adopts a non-continuous image taking method, the response to color is different to human eyes. The main reason resides on that the transmittance of infrared is higher than the transmittance of visible lights, so that it is necessary to remove the portion of infrared that can be detected by the image sensor but not by human eyes, while adjusting the response to color in the range of visible lights, and the color of the image can match with the feeling of human eyes. Therefore, one of the main factors for an image reception device affecting the quality of the optical lens assembly for image taking is how to filter infrared light effectively without affecting the chromatic aberration and image aberration. To prevent the color shift problem occurred after receiving the infrared light by the CCD and CMOS image sensors, the prior art generally uses a low-pass light filter (LPLF) to absorb or reflect lights of the infrared band. As disclosed in U.S. patent and publication of US2009/0009888 and U.S. Pat. No. 7,513,704, the low-pass light filter is installed between a lens assembly and an image sensor if the infrared isolation filter is used. As disclosed in U.S. Pat. No. 6,754,009, and U.S. Pat. Publication No. 2008/0266670, an infrared isolation filter is installed between the lens assemblies.
The low-pass light filter is generally made by plating a layer of coating onto blue glass or plate glass, wherein the blue glass is a glass manufactured by adding sodium oxide, magnesium oxide, calcium oxide, cobalt oxide and a small quantity of rare earth oxides for absorbing lights with a wavelength other than those of 400 nm˜700 nm, or the light of different bands is adjusted according to the added metal oxide, so as to further improve the absorbing effect within the wavelength bands of UV and infrared light. The plate glass plated coating is a plated coating formed on the glass substrate for reflecting or absorbing the infrared light as disclosed in U.S. Pat. No. 7,166,359.
At present, the low-pass filter technology has been applied to sunglasses, contact glasses or measurement instruments as disclosed in U.S. Pat. No. 5,149,182 or U.S. Pat. Publication No. US2008/0137030. For applications of the optical lens assembly for image taking as disclosed in U.S. Pat. No. 7,064,909 or U.S. Pat. Publication No. US2009/0097103, a two-lens or multi-lens optical lens assembly for image taking can be used for filtering influential lights such as the infrared light and can be manufactured easily, therefore, blue glass is used directly for manufacturing the lenses. Although this method can achieve the effect of filtering the infrared light, the blue glass changes the Abbe number of the lens elements which is unfavorable for correcting chromatic aberrations and image aberrations.
In recent years, electronic products such as digital still cameras, mobile phone cameras and web cameras tend to be developed with a compact design, and users have an increasingly stricter requirement on the quality and the resolution of the image reception devices in addition to the requirement for a compact and low-cost image reception device, while meeting the requirement of an optical lens assembly for image taking with good aberration correction ability, high resolution and high image quality. The conventional optical lens assembly for image taking, an infrared isolation filter is installed, regardless of being installed between the lens assemblies or in front of the image sensor, the infrared isolation filter simply has the effect of filtering the infrared light, but the optical design of the optical lens assembly for image taking is still designed with a full spectrum, and thus the correction of the image, aberration, and color shift still require further improvements. If the infrared light is filtered and an image is formed at the image sensor, the optical design is still insufficient for a high-quality and high-resolution optical lens assembly for image taking.
Therefore, the present invention provides a more practical design and uses a front IR-filter to adjust the rear focal length appropriately and shorten the whole optical system, and adopts an absorbing filter such as the blue glass or with a coating thereof to provide a good effect of absorbing lights at the infrared band to reduce the color shift effectively. Moreover, with the appropriate design of the optical lens assembly for image taking, the length of the optical lens assembly for image taking is shortened, and a high-resolution, high-quality aberration and color shift correction capability is provided for the application to electronic products.